An AC (alternating current) electric power transmission is applied to most conventional electric power systems because of a convenience of an AC voltage transformation, by using an electromagnetic field as an energy transmission medium and achieving voltage transformation, especially the transformation from a low voltage to a high voltage, according to an electromagnetic induction principle by coupling a primary coil and a secondary coil with different numbers of turns. Compared with an AC, a DC has huge advantages in terms of a transmission loss, a stability of a grid and a cost. For a DC voltage transformer, particularly for a DC voltage step-up transformer, however, a simple and efficient boosting technology and a device thereof have not been proposed for a long time. With a technology development, in one aspect, power generation technologies such as a solar cell or a fuel cell, which directly generate DC electric power, hold a larger and larger proportion to the whole electric power of the world; in another aspect, electric equipments such as LED bulbs, OLED, LED TVs, LED displays and other household electric appliances which use a DC electric power are increasing. A usual scheme of DC power generation, transmission and application, which is complex and explained as “DC power generation, conversion from DC to AC, AC transformation, AC high voltage transmission, AC transformation, conversion from AC to DC, and then DC application”, has following disadvantages.
1. A required apparatus has complicated structure, numerous elements, large volume and high cost.
2. There is energy loss to different extents in each procedure, such as voltage transformation loss, current transformation loss, transmission loss, drive loss resulting from reconversion to DC at a user side, etc., thus causing low total energy transmission efficiency
3. During a process of AC high voltage transmission, it is difficult to allow a complete synchronization of AC phases among different power generation systems, thus causing a serious stability problem of the whole power grid.
In contrast, a scheme of “DC power generation, DC transformation, DC high voltage transmission, DC transformation, and then DC application” is simpler, more stable, and more reliable, and has less energy loss. In order to popularize the DC power generation and transmission, developments of DC transformation technologies and DC transformers are becoming a focus.